In order to achieve a reduction in pollutants, several methodologies and measures have been adopted by legislators, academia and industry. Research laboratories and manufacturers are focusing, among others, on the use of fuel blends with a variety of physical and chemical properties. Among these fuels oxygenates have been widely investigated because of the possibility of suppressing the CAC bonds and therefore the soot precursor species with the consequence of reducing soot emissions from diesel engines. In particular, poly (oxymethylene) dimethyl ethers (POMDME or OME in abbreviated form) are characterized by a CH₃—O—(CH₂—O)_n—CH₃ general structure, with a mass fraction of oxygen within the molecule up to 50%.

… The aim of the present work is to investigate, in a single cylinder “heavy duty” direct injection diesel engine, a mixture of POMDMEs blended into commercial diesel in order to examine achievable engine performance and exhaust emissions taking into account not only particulate matter but nitrogen oxides and carbon dioxide as well. … A production on industrial scale of POMDME to be blended with commercial diesel would be of interest in order to obtain blends characterized by diesel high energy content and POMDME strong capability of reducing soot formation.

—Iannuzzi et al.

The single-cylinder engine (located at ETH Zurich) is based on an MTU 396 series engine and features a common rail injector system capable of pressure up to 1600 bar and an 8-hole injector.

The team compared the reference diesel fuel with two blends of 90% diesel - 10% POMDME by volume and 95% diesel-5% POMDME by volume. The POMDME used was composed of 41.51 wt% OME2; 15.50 wt% OME3; 27.52 wt% OME4; 8.74 wt% OME5; 4.58 wt% OME6; 2.15 wt% OME7; and 0.55 wt% Methylal, 0.07 wt% Methanol, 0.05 wt% Ethanol, 0.33 wt% Trioxane.

The POMDME fuel presented an oxygen overall mass fraction of 0.46 g/g, and energy content of 20 MJ/kg. The two blends are characterized by an oxygen mass fraction of 2.74 and 5.44 wt%. The POMDME mixture was synthesized at the University of Kaiserslautern.

Testing was done at 1050 rpm at the constant values of 8 and 10.5 bar BMEP.

Their main conclusions:

• The 10% POMDME in diesel blend can reduce soot emissions up to 34% compared to a baseline diesel, under operating conditions with similar premixed–diffusive combustion mode ratios.

• NO_x emissions were not significantly affected by the adoption of blends containing a percentage of oxygenated fuel up to 10%.

• A 2.2% and a 4% increase (with respect to commercial diesel) in BSFC have been detected with 5% POMDME and 10% POMDME respectively. On the other hand, no significant decay in thermal efficiency has been detected with the investigated blends.

The main characteristics, in addition to their strong ability in reducing soot emissions, that could play a significant role in pushing POMDMEs towards an industrial scale production mainly refer, on one side, on the fact that these fuels are characterized by similar physical and chemical properties with respect to commercial diesel allowing their use in existing engines without modifications in the injection system; on the other side POMDMEs can be obtained from natural gas or from electric power through carbon dioxide activation in a sustainable way and this determines an important advantage with respect to oil-based products. Of course fuel economy plays a major role in considering alternative fuels production on industrial scale and therefore, even though they appear to be interesting for environ- ment protection, further investigation should be carried on in order to determine, in the whole range of the engine operative conditions, weather the use of such fuels could be concretely proposed on the market.

—Iannuzzi et al.

Resources

• Stefano Emanuele Iannuzzi, Christophe Barro, Konstantinos Boulouchos, Jakob Burger (2017) “POMDME-diesel blends: Evaluation of performance and exhaust emissions in a single cylinder heavy-duty diesel engine,” Fuel, Volume 203, Pages 57-67 doi: 10.1016/j.fuel.2017.04.089